Toner for electrostatic development and its fabrication method by treatment of suspension with reverse-neutralization

ABSTRACT

The present invention relates to a toner for electrostatic development produced by a suspension process accompanied with reverse-neutralization and the making method thereof. The making method of a toner for use in electrostatic development according to the present invention comprises a phase for producing a linear low molecular weight polymer having carboxyl groups (—COOH) at the end of a polymer chain; a phase for producing a cross-linked high molecular weight water-dispersible latex; a phase for producing colored resin dispersions by adding a colorant, charge control agents, release agents and the cross-linked high molecular weight water-dispersible latex; a phase for producing toner particles through a suspension process accompanied with reverse-neutralization; a phase for producing a colored toner particle composition through filtrating, washing and vacuum drying; and a phase for adding hydrophobic silica to the colored toner particle composition, and blending them using a powder mixer.

TECHNICAL FIELD

The present invention relates to a toner for electrostatic development produced by a suspension process accompanied with reverse-neutralization and the making method thereof, and more particularly, to a toner produced by a suspension treatment accompanied with reverse-neutralization for a low molecular weight linear polymer with carboxyl groups at the end of a polymer chain and the making method thereof.

BACKGROUND ART

In a electrophotography or a electrostatic recording, there is formed an electrostatic latent image on a photo-conductor by a charging and a exposure process, and the latent image is developed by a developer and transferred to media, thereby being visualized as an image through a fusing process. Here, whether a clear image with excellent quality can be generated depends on various conditions in a developing and a fusing process. In a developing process, the quality of developed image is determined by electrical characteristics and a particle size of toner adhered to a latent image, and a degree of dispersion of various additives in a toner composition. In a fusing process, the image quality is determined by melt characteristics of toner fused and a degree of release property. Accordingly, the improvement of toner performance is required continuously.

There are a polymerization and a crushing method in making methods of toner. In the crushing method, there are mixed a binder resin, a colorant, charge control agents and release agents in a kneader, and, then, the mixture is heated, melted and crushed, thereby producing a toner. However, in the crushing method, it is impossible to disperse finely particles and, therefore, the additives are not able to function rightly. Moreover, the yield of product having a desirable particle size is low because a range of particle distribution is broad, and toner performance tends to be poor because spherical particles are not produced.

There are emulsion aggregation and suspension polymerization in the polymerization method. The emulsion aggregation method comprises making latex through a emulsion polymerization of polymerizable monomer; mixing it with a colorant, charge control agents, release agents and so on; and heating them over several hours to tens hours with continuous agitation so that emulsion particles are aggregated, thereby forming desirable particles with a particular size. Examples of such method are disclosed in Japanese Patent Publication Nos. 63-282752, 63-282756 and 06-250439, U.S. Pat. Nos. 5,352,521, 4,996,127 and 4797339, Korean Patent Publication Nos. 1997-066730 and 1998-073192, and Korean Patent No. 0340303. However, the emulsion aggregation has a broad range of particle distribution and cannot produce fine particles because it is carried out through a long-running aggregation process. Another problem is poor fusing property due to a large molecular weight and high fusing point elasticity.

The suspension polymerization comprises pre-mixing monomers with a colorant, charge control agents and release agents; dispersing them using high shear force to form monomer drops, which can provide desirable particle diameters; adding a stabilizer and polymerizing them; and precipitating formed polymers to obtain polymer particles. An advantage of the suspension polymerization is to be able to produce fine particles of toner. Examples of such method are disclosed in Japanese Patent Publication Nos. 61-118758, 07-128909, and 09-311503, U.S. Pat. Nos. 5,219,697 and 5,288,577, Korean Patent Publication No. 2000-057424, and Korean Patent Nos. 0341786 and 285183. However, the conventional suspension polymerization method has several problems. For one thing, it is difficult to adjust degree of polymerization because additives counteract polymerization reaction. Moreover, defectives can be produced by abnormal reactions due to instability. Another disadvantage is a poor fusing property due to a high softening point of the produced toner particles.

DISCLOSURE OF INVENTION

Accordingly, the present invention is directed to a toner for electrostatic development and the making method thereof that substantially obviates one or more problems due to limitations and disadvantages of the related art. The making method of toner according to the present invention is composed of making a linear low molecular weight polymer having carboxyl groups at the end of a polymer chain, which can be easily dispersed in water due to reaction of a functional group of the molecular with a basic compound; making a water-dispersible resin composition using the linear low molecular weight polymer; and producing a toner with fine particles and a narrow range of particle distribution through a suspension process accompanied with reverse-neutralization. An object of the present invention is to provide a making method of a toner that has excellent fusing and separation property and desirable offset property, and that does not generate fog and deterioration of toner according to wear by use, thereby providing a high quality image.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a flow chart of a making method of a toner for electrostatic development by a suspension process accompanied with reverse-neutralization in accordance with the present invention;

FIG. 2 is a flow chart of a making method of a toner for electrostatic development by a suspension process accompanied with reverse-neutralization according to another embodiment of the present invention; and

FIG. 3 is a flow chart of a making method of a toner for electrostatic development by a suspension process accompanied with reverse-neutralization using a reclaimed polyester resin.

BEST MODE FOR CARRYING OUT THE INVENTION

A making method of a toner for use in an electrostatic development by a suspension process accompanied with reverse-neutralization comprises:

-   -   a phase for producing a linear low molecular weight polymer         having carboxyl groups (—COOH) at the end of a polymer chain;     -   a phase for producing a water-dispersible resin composition to         function as a dispersant by adding basic compounds to the linear         low molecular weight polymer to neutralize them and adding         distilled water;     -   a phase for producing a cross-linked high molecular weight         water-dispersible latex, separately;     -   a phase for producing colored resin dispersions by adding a         colorant, charge control agents, and release agents to the         water-dispersible resin composition, dispersing them using high         shear force, adding the cross-linked high molecular weight         water-dispersible latex, and mixing and dispersing the         cross-linked latex;     -   a phase for producing toner particles by putting the colored         resin dispersions into an aqueous solution containing acid         compounds to carry out a suspension process accompanied with         reverse-neutralization using high shear force, and heating and         stabilizing the solution;     -   a phase for producing a colored toner particle composition by         filtrating and washing the toner particles two or three times,         repeatedly, and carrying out vacuum drying; and     -   a phase for adding hydrophobic silica to the colored toner         particle composition, and blending them using a powder mixer.

Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

FIG. 1 is a flow chart of a making method of a toner for electrostatic development by a suspension process accompanied with reverse-neutralization in accordance with the present invention. As shown in FIG. 1, the making method of a toner for electrostatic development comprises:

-   -   phase 1 for producing a linear low molecular weight polymer         having carboxyl groups (—COOH) at the end of a polymer chain;     -   phase 2 for producing a water-dispersible resin composition to         function as a dispersant by adding basic compounds to the linear         low molecular weight polymer to neutralize and adding distilled         water;     -   phase 3 for producing a cross-linked high molecular weight         water-dispersible latex, separately;     -   phase 4 for producing colored resin dispersions by adding a         colorant, charge control agents, and release agents to the         water-dispersible resin composition from the phase 2, dispersing         them using high shear force, adding the cross-linked high         molecular weight water-dispersible latex from the phase 3, and         mixing and dispersing the cross-linked latex;     -   phase 5 for producing toner particles by putting the colored         resin dispersions from the phase 4 into an aqueous solution         containing acid compounds to carry out a suspension process         accompanied with reverse-neutralization using high shear force,         and heating and stabilizing the solution;     -   phase 6 for producing a colored toner particle composition by         filtrating and washing the toner particles from the phase 5 two         or three times, repeatedly, and carrying out vacuum drying; and     -   phase 7 for adding hydrophobic silica to the colored toner         particle composition from phase 6, and blending them using a         powder mixer.

If the particles of the colored toner particle composition from the phase 6 are bad, the particles are filtrated and inputted to the phase 2, and are retreated according to the same processes mentioned above.

The linear low molecular weight polymer from the phase 1 is produced by a solution polymerization method. The solution polymerization method comprises to dissolve monomers in an inactive solvent and to polymerize the monomers in the solution under an appropriate solvent-soluble catalyst. The monomers to be used in the present invention can be selected from the group of aromatic vinyl-based monomers, acrylate monomers, and monomers possible to copolymerize with the aromatic vinyl-based monomers or acrylate monomers. Examples of suitable aromatic vinyl-based monomers include styrene, methyl styrene, dimethyl styrene, and halogenated styrene. The amount of the aromatic vinyl-based monomer to be used is 20˜80 w %, based on the total amount of the monomer mixture. Examples of suitable acrylate monomers include methyl(meta) acrylate, butyl acrylate, 2-ethyl hexyl acrylate, acrylic acid, meta acrylic acid and glycidyl meta acrylate. The amount of the acrylate mononer to be used is 5˜50 w %, based on the total amount of the monomer mixture. Examples of monomers possible to copolymerize with the monomers mentioned above include acrylonitrile butadiene and meta arcylonitrile, and the amount of the monomer to be used is 5˜50 w %, based on the total amount of the monomer mixture. The proportion of the monomers to be used is adjusted according to fusing property of a toner, a softening point in view of the melting property and a glass transition temperature. The solvents to be used at the solution polymerization can be selected from the group of alcohols, ketones, cellsolves, tetrahydrofuran, n-methylpyrrolidone, dimethyl formamide, and a mixture thereof. The amount of the solvent to be used is 20˜100 w %, based on the total amount of the monomer mixture. The solvent used can be completely eliminated by decompression after finishing the polymerization reaction. Polymerization initiators to be used can be selected from the group of benzoyl peroxide, 2,2-azobis isobutyronitrile, dimethyl 2,2-azobis(2-methyl propionate), 2,2-azobis(2,4-dimethyl valeronitrile), di-t-butyl peroxide, dicumyl peroxide, lauroyl peroxide and t-butalperoxi-2-ethyl hexanoate. The amount of the polymerization initiator to be used is 0.01˜3 w %, based on the total amount of the monomer mixture. As the polymerization initiator, oil-soluble radical initiators are more preferable. Molecular weight controllers to be used can be selected from the group of t-dodecyl mercaptan, n-dodecyl mercaptan, n-octyl mercaptan, carbon tetrachloride and carbon tetrabromide. The amount of the molecular weight controller to be used is 0.01˜10 w %, based on the total amount of the monomer mixture. The resultant linear low molecular weight polymer has a number-average molecular weight of 5,000˜50,000 and an acid value of 10˜110 mg KOH/g.

In addition, a linear low molecular weight polyester resin composition can be produced from the phase 1, and, therefore, a polyester resin toner can be produced using it. The linear low molecular weight polyester resin composition is a polymer having an acid value of 10˜110 mg KOH/g. The linear low molecular weight polyester resin can be produced by using excess of polybasic acids in a reaction of polybasic acids with polyhydric alcohols, and the making method thereof comprises to produce a linear low molecular weight polyester resin composition through a first reaction, which produce a low molecular weight polymer using a linear structure forming accelerant, and to carry out a second reaction by adding polybasic acids to it so that the polyester resin has two or three carboxyl groups at the end of a polymer chain.

Here, on the contrary, said polyester resin composition can be produced from depolymerizing a waste polyester resin to carry out an addition reaction so that the polyester resin has two or three carboxyl groups at the end of a polymer chain. Specially, as shown in FIG. 3, the polyester resin composition can be produced by depolymerizing a waste polyester resin using a solid resin dissolvent, carrying out an addition reaction accompanied with a second depolymerization using polybasic acids, and causing polycondensation reaction through adding polyhydric alcohols under a tin based catalyst. The making method of a toner using a waste polyester resin will be explained at Example 8 in detail.

In the making method of said polyester resin composition, materials to facilitate linear structure and to induce the formation of a low molecular weight polymer can be selected from the group of rosin, wood rosin, rosin derivatives, terpen-based resins, petroleum resin and derivatives thereof, dicyclopentadien (hereinafter referred to as “DCPD”) and derivatives thereof gum rosin, dehydrogenated rosin, hydrogenated rosin, maleic rosin, rosin ester, pinene resin, dipentene resin, C5 petroleum resins, C9 petroleum resins, dammar resin, copal resin, DCPD resin, hydrogenated DCPD resin, styrene maleic resin, and a mixture thereof. The amount of the material to be used is 10˜100 w %, based on the total amount of monomers.

Examples of polybasic acids to be used include phthalic anhydride, isophthalic acid, terephthalic acid, adipic acid, azelaic acid, sebacic acid, tetrahydro phthalic anhydride, maleic anhydride, fumaric acid, itaconic acid, trimellitic anhydride, pyromellitic anhydride, benzoic acid, and a mixture thereof. The amount of the polybasic acid to be added is 10˜90 w %, based on the total amount of monomers. Examples of the polyhydric alcohols to be used include ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, polyethylene glycol, alkylene oxide adduct of bisphenol A, trimethylol propane, glycerin, pentaerythritol, and a mixture thereof. The amount of the polyhydric alcohol to be used is 10˜90 w %, based on the total amount of monomers. As a catalyst, metal organic acid or tin based catalysts can be used at the amount of 0.05˜0.5 w %, based on the total amount of monomers. In order to combine carboxyl groups to the end of a polymer chain, there can be selected trimellitic anhydride, trimellitic acid, pyromellitic anhydride, pyromellitic acid, maleic anhydride, maleic acid, fumaric acid, adipic acid, benzoic acid, sebacic acid, maleic rosin, maleic styrene, maleic isobutylene, and a mixture thereof at the amount of 10˜70 w %, based on the amount of the polyester resin composition.

In the phase 2, a water-dispersible resin composition to function as a dispersant is produced by neutralizing the linear low molecular weight polymer using basic compounds, and adding distilled water. Examples of suitable basic compounds to be used include sodium hydroxide, potassium hydroxide, ammonium hydroxide, lithium hydroxide, and amines. The amount of the basic compound to be used is 5˜50 w %.

In the phase 3, a cross-linked high molecular weight water-dispersible latex is produced by emulsion polymerization, which emulsifies monomers in water containing a water-soluble catalyst and emulsifier and polymerizes them. There are used 20˜90 w % of styrene, 5˜90 w % of acrylate-based monomer and 5˜50 w % of cross-linked monomer. Examples of suitable anionic surfactants to be used include sodium stearate, sodium lauryl sulfate, sodium dodecylbenzene sulfonate, and a mixture thereof. The amount of the anionic surfactant to be used is 1˜20 w %, based on the total amount of the monomer mixture. Examples of suitable nonionic surfactants to be used include poly(oxyethylene) nonyl phenyl ether, octyl methoxy polyethyl oxyethanol, sorbitan lauryl ethylene oxide adduct and a mixture thereof. The amount of the nonionic surfactant to be used is 1˜30 w %, based on the total amount of the monomer mixture. Examples of suitable water-soluble initiators to be used include potassium persulfate, ammonium persulfate, sodium bisulphate and sodium bicarbonate. The amount of the water-soluble initiator to be used is 0.01˜2 w %, based on the total amount of the monomer mixture. The resultant cross-linked high molecular weight water-dispersible latex has a gel content of 5˜50 w % and a weight average molecular weight of 100,000˜1,000,000.

In the phase 4, there are produced colored resin dispersions by using the water-dispersible resin composition from the phase 2, the cross-linked high molecular weight water-dispersible latex from the phase 3, a colorant, charge control agents and release agents. Examples of suitable colorants include black pigments such as carbon black, acetylene black and magnetite, yellow pigments such as iron oxide yellow, hansa yellow and permanent yellow, blue pigments such as phthalocyanine blue and violet, red pigments such as iron oxide red, carmine, toluidine red and quinacridone red, and green pigments such as phthalocyanine green and chrome green. The amount of the colorant to be used is 1˜50 w %, based on the amount of a binder resin. The suitable charge control agents can be selected from the group of negrosin, quaternary ammonium salts, salicylic acid-based metal salts and metal-azo compounds (e.g., BONTRON N-01, BONTRON N-07, BONTRON S-24 and BONTRON E-84 available from Orient Chemical(Korea), Ltd.). The amount of the charge control agents to be used is 0.5˜15 w %, based on the amount of a binder resin. The suitable release agents can be selected from the group of paraffin wax, polyethylene wax, carnauba wax, montan wax, ester wax and Sasol wax. The amount of the release agents to be used is 1˜30 w %, based on the amount of a binder resin.

In the phase 5, there are produced toner particles by a suspension process accompanied with reverse-neutralization using acid compounds. The suitable acid compounds can be selected from the group of hydrochloric acid, sulfuric acid, nitric acid, acetic acid, formic acid, oxalic acid, fluoric acid, phosphoric acid, bromic acid, and p-toluene sulfonic acid. The amount of the acid compound to be used is 5˜50 w %, based on the amount of the colored resin dispersions. In the phase 7, the amount of hydrophobic silica, as an external additive, to be used is 1˜5 w %, based on 100 g of the colored toner particle composition from the phase 6.

The making method of a toner for electrostatic development will be described in further detail with reference to the examples thereof, which examples however are merely intended to be illustrative and not to be construed as limiting the scope of the invention.

EXAMPLE 1 Method for Making a Water-Dispersible Resin Composition

There are prepared 150 grams of ethyl cellsolve, 250 grams of styrene, 120 grams of ethyl hexyl acrylate, 60 grams of acrylic acid, 30 grams of styrene-isoprene diblock copolymer, 1.1 grams of n-dodecyl mercaptan, and 0.5 grams of azobis isobutyronitrile (hereinafter referred to as “AIBN”). A reactor equipped with an agitator, a reflux condenser, a thermometer and a nitrogen injection port is charged with 2/10 of the mixture of the reactants, and heated to 125° C. and maintained at that temperature with stirring over forty-five minutes. The resultant product is a seed polymer. Then, the rest mixture is little by little added to the reactor slowly, over a 3-hour period at 130° C., and the reactants are heated to 125° C. and maintained over 6 hours at that temperature. The product is diluted by 150 grams of ethyl cellsolve. The resultant polymer has 75 mg KOH/g of acid value, 35° C. of glass transition temperature, and 11,000 of weight average molecular weight. Finally, there is produced a water-dispersible resin aqueous solution by adding 100 grams of 20% sodium hydroxide solution to said polymer, carrying out polymerization reaction over thirty minutes at 85° C., and diluting them with 300 grams of distilled water.

EXAMPLE 2 Another Method for Making a Water-Dispersible Resin Composition

A reactor equipped with an agitator, a reflux condenser, a thermometer and a nitrogen injection port is charged with 150 grams of butyl cellsolve, 250 grams of styrene, 120 grams of butyl acrylate, 60 grams of acrylic acid, 1.1 grams of n-dodecyl mercaptan and 0.5 grams of AIBN. The reaction method is the same with Example 1. The resultant polymer, having an acid value of 81 mg KOH/g, a glass transition temperature of 59° C. and a weight average molecular weight of 9,000 is solubilized and become a water-dispersible resin aqueous solution.

EXAMPLE 3 Method for Making a Cross-Linked High Molecular Weight Water-Dispersible Latex

There are prepared 100 grams of styrene, 100 grams of methyl meta acrylate, 100 grams of ethyl acrylate, 6 grams of acrylic acid and 10 grams of divinyl benzene. The mixture of said reactants is little by little added to a solution, which is comprised of 9 grams of anionic emulsifier, 16 grams of nonionic emulsifier and 190 grams of distilled water, to form preemulsion. Another reactor is charged with 4 grams of anionic emulsifier, 8 grams of nonionic emulsifier, 1.5 grams of potassium persulfate and 200 grams of distilled water, and heated to 80° C. Said preemulsion is little by little added to the second reactor slowly and polymerized over 3 hours at 80° C. The second reactor is then raised to 90° C., and a solution which 1.5 grams of sodium bisulphate is dissolved in 30 grams of distilled water, is little by little added to the second reactor slowly to cause the reactants to react over 5 hours continuously. Said processes are carried out in reactors equipped with an agitator, a reflux condenser, a thermometer and a nitrogen injection port. The resultant cross-linked high molecular weight latex emulsion has a glass transition temperature of 65° C., a weight average molecular weight of 300,000 and a gel content of 45%.

EXAMPLE 4 Another Method for Making a Cross-Linked High Molecular Weight Water-Dispersible Latex

A mixture composed of 250 grams of styrene, 120 grams of butyl acrylate, 7 grams of acrylic acid and 15 grams of divinyl benzene is little by little added to a solution composed of 10 grams of anionic emulsifier, 16 grams of nonionic emulsifier, and 190 grams of distilled water, to form preemulsion. Another reactor is charged with 5 grams of anionic emulsifier, 8 grams of nonionic emulsifier, 1.5 grams of potassium persulfate and 200 grams of distilled water, and heated to 80° C. The rest process is the same with Example 3. The resultant cross-linked high molecular weight latex emulsion has a glass transition temperature of 55° C., a weight average molecular weight of 350,000 and a gel content of 35%.

EXAMPLE 5 Method for Making a Toner for Electrostatic Development Using the Compositions from said Examples

A mixture composed of 3 grams of carbon black(PRINTEX 150 T), 0.5 grams of charge control agent(BONTRON S-34), and 30 grams of distilled water is added to the water-dispersible resin aqueous solution from Example 1 and dispersed by a fast distributor to form colored resin dispersions. Release agents are added and dispersed in the colored resin dispersions. Another reactor is charged with an aqueous solution composed of 5 grams of hydrochloric acid and 100 g grams of distilled water. Then, the colored resin dispersions are slowly added to the reactor. The mixture is stilted fast at 50° C. so that toner particles are formed by a suspension process accompanied with reverse-neutralization. The resultant potato-shaped toner particles have 9 μm of particle diameter and 1.29 GSD of average volume diameter. The toner particles are washed, filtrated, and dried. Then, 100 grams of the dried toner particle composition is mixed with 1 gram of hydrophobic silica(Degussa R972) by means of Henschel mixer to produce a toner for electrostatic development. A rebuilt toner cartridge (Laser printer ML 6060 made in Samsung Electronics Co., Ltd) filled with said toner provides a very clear and high quality image.

EXAMPLE 6 Another Method for Making a Toner for Electrostatic Development

A mixture composed of 3 grams of carbon black(PRINTEX 150 T), 0.5 grams of charge control agent(BONTRON S-34), and 30 grams of distilled water is added to the resin solution from Example 2 and dispersed by a fast distributor to form colored resin dispersions. The colored resin dispersions are mixed with 50 grams of the cross-linked high molecular weight water-dispersible latex from Example 3. The mixture is again dispersed to form colored resin dispersions. Another reactor is charged with a solution, which 3.5 grams of hydrochloric acid is mixed with 100 grams of distilled water. Then, the colored resin dispersions are slowly added to the reactor with fast stirring at 50° C. so that toner particles are formed by a suspension process accompanied with reverse-neutralization. The resultant potato-shaped toner particles have 7 μm of particle diameter and 1.27 GSD of average volume diameter. The toner particles are washed, filtrated, and dried. Then, 100 grams of the dried toner particle composition is mixed with 1 gram of hydrophobic silica(Degussa R972) by means of Henschel mixer to produce a toner for electrostatic development. A rebuilt toner cartridge (Laser printer ML 6060 made in Samsung Electronics Co., Ltd) filled with said toner provides a very clear and high quality image.

EXAMPLE 7 Preparation of a Toner by a Suspension Process Accompanied with Reverse-Neutralization

FIG. 2 shows a method for making a toner for electrostatic development by a suspension process accompanied with demineralization reaction using a polyester resin which has low melt elasticity, excellent adhesive property, and excellent low temperature fix characteristics such as exfoliation resistance.

As shown in FIG. 2, the making method of a toner for electrostatic development comprise:

-   -   phase 1 for producing a linear low molecular weight polyester         resin composition having carboxyl groups (—COOH) at the end of a         polymer chain;     -   phase 2 for producing a polyester resin aqueous solution to         function as a dispersant by adding basic compounds and distilled         water to the low molecular weight polyester resin composition;     -   phase 3 for producing a cross-linked ethylene-based         copolymerization latex;     -   phase 4 for producing colored resin dispersions by mixing the         polyester resin aqueous solution from the phase 2 with a         colorant, charge control agents, and release agents, adding the         cross-linked ethylene-based copolymerization latex from the         phase 3, and mixing and dispersing the cross-linked latex;     -   phase 5 for producing toner particles by putting the colored         resin dispersions from the phase 4 into an aqueous solution         containing acid compounds to carry out a suspension process         accompanied with demineralization reaction using high shear         force, and heating the solution;     -   phase 6 for producing a colored toner particle composition by         filtrating and washing the toner particles from the phase 5, and         carrying out vacuum drying; and     -   phase 7 for adding hydrophobic silica or titanium oxide to the         colored toner particle composition from the phase 6 at the         amount of 1˜5 w %, and blending them using a powder mixer.

The resultant polyester resin toner has 5˜15 μm of particle size and a narrow range of particle distribution. Here, the linear low molecular weight polyester resin composition having carboxyl groups at the end of a polymer chain from the phase 1 is the same with that according to the making method of the present invention, and the rest process and ingredients to be used is the same with other Examples according to the present invent.

EXAMPLE 8 Preparation of a Toner by Using Waste Polyester Resin

A polyester resin composition having two or three carboxyl groups at the end of a polymer chain is used as a stating material. The polyester resin composition is prepared by depolymerizing a waste polyester resin to carry out an addition reaction. FIG. 3 is a flow chart according to the making method of Example 8. As shown in FIG. 3, the making method of a toner by using a waste polyester resin comprise:

-   -   phase 1 for producing a linear low molecular weight polyester         resin composition using a waste polyester resin so that the         linear low molecular weight polyester resin has carboxyl groups         at the end of a polymer chain;     -   phase 2 for producing a polyester resin aqueous solution by         neutralizing the polyester resin composition from the phase 1         using an aqueous solution containing basic compounds, and         dissolving the composition in water, water-friendly solvents or         a mixture of both of them;     -   phase 3 for producing a cross-linked ethylene-based         copolymerization latex, separately;     -   phase 4 for producing colored resin dispersions by adding a         colorant, charge control agents, and release agents to the         polyester resin aqueous solution from the phase 2, adding the         cross-linked ethylene-based copolymerization latex from the         phase 3, and mixing and dispersing the cross-linked latex;     -   phase 5 for producing toner particles by putting the colored         resin dispersions from the phase 4 into an aqueous solution         containing acid compounds to carry out a suspension process         accompanied with demineralization reaction using high shear         force, and heating the solution;     -   phase 6 for producing a colored toner particle composition by         filtrating and washing the toner particles from the phase 5 and         carrying out vacuum drying; and     -   phase 7 for adding hydrophobic silica or titanium oxide to the         colored toner particle composition from phase 6 at the amount of         1˜5 w %, and blending them using a powder mixer.

The resultant polyester resin toner has 5˜15 μm of particle size and a narrow range of particle distribution. In the phase 1, a waste polyester resin is depolymerized first by a solid resin dissolvent. Then, an addition reaction accompanied with second depolymerization is carried out using polybasic acids. Subsequently, polyhydric alcohols are added to the depolymerization composition and a polycondensation reaction is carried out using a tin-based catalyst. The resultant polyester resin composition has an acid value of 10˜110 mg KOH/g, a weight average molecular weight of 3,000˜50,000, and a softening point of 70˜150° C. The solid resin dissolvent to be used in the phase 1 is selected from the group of gum rosin, wood rosin, dehydrogenated rosin, hydrogenated rosin; maleic rosin, rosin ester, pinene resin, dipentene resin, C5 petroleum resins, C9 petroleum resins, dammar resin, copal resin, dicyclopentadien(hereinafter referred to as “DCPD”) resin, hydrogenated DCPD resin, styrene maleic resin, and a mixture thereof. The weight ratio of the waste polyester resin to the solid resin dissolvent is preferably 1:9˜9:1. The processes and ingredients to be used in Example 8 are the same with those in the making method according to the present invent, except phase 1 to depolymerize a waste polyester resin as a starting material. The resultant toner has 5˜10 μm of particle diameter and 1.05˜1.35 GDS of average volume diameter. The Example 8 will be described in further detail by referring to preparation examples, which examples however are merely intended to be illustrative and not to be construed as limiting the scope of the invention.

PREPARATION EXAMPLE 1

Crushed waste polyethylene terephthalate(hereinafter referred to as “PET”) chips (400 g), gum rosin (200 g) and monobutyl tartaric acid (0.3 g) are placed in a reactor which is equipped with an agitator, a reflux condenser, a separator, a thermometer and a nitrogen injection port. The mixture is heated to 250° C. and maintained at that temperature over 2 hours under a nitrogen atmosphere. The mixture is stirred when it begin to be melted. After the mixture changes into a transparent state, the reactor is cooled to 150° C., and then, maleic anhydride (180 g) is added to the reactor. When the temperature of the mixture reaches to the point that ring-opening reaction is finished, the mixture is again heated to 235° C. and maintained at that temperature over 3 hours. The resultant depolymerization product has an acid value of 115 mg KOH/g. Then, ethylene oxide adduct of bisphenol A (200 g) is added to the depolymerization product, and the mixture is maintained at 250° C. over 5 hours to carry out dehydration and polycondensation reaction. When an acid value of the product reaches to 55 mg KOH/g, the reactor is cooled and charged with 50 grams of sodium hydroxide and 1,500 grams of distilled water. Then, the mixture is stirred over thirty minutes at 85° C. The resultant water-soluble polyester resin(hereinafter referred to as “resin solution A”) has an acid value of 39 mg KOH/g, a weight average molecular weight of 11,000, a softening point of 80° C. and pH of 8.5.

A mixture composed of 3 grams of carbon black(PRINTEX 150T), 0.5 grams of charge control agent(BONTRON S-34), and 30 grams of distilled water is added to 100 grams of the resin solution A and dispersed by a fast distributor to form colored resin dispersions. The colored resin dispersions is mixed with release agents and again dispersed. Another reactor is charged with an aqueous solution which 5 grams of hydrochloric acid is mixed with 100 grams of distilled water. Then, the colored resin dispersions are slowly added to the reactor with fast stirring at 50° C. so that toner particles are formed by a suspension process accompanied with reverse-neutralization. The resultant potato-shaped toner particles have 9 μm of particle diameter and 1.29 GSD of average volume diameter. The obtained toner particles are washed, filtrated, and dried. Subsequently, 100 grams of the dried toner particle composition is mixed with I gram of hydrophobic silica(Degussa R972) by means of Henschel mixer to produce a toner for electrostatic development. A rebuilt toner cartridge (Laser printer ML6060 made in Samsung Electronic Co., Ltd) filled with said toner provides a very clear and high quality image.

PREPARATION EXAMPLE 2

Crushed waste PET chips (400 g), hydrogenated rosin (200 g), monobutyl tartaric acid (0.3 g), trimellitic anhydride (150 g) and neopentyl glycol (200 g) are placed in a reactor which is equipped with an agitator, a reflux condenser, a separator, a thermometer and a nitrogen injection port. The reaction method is the same with Preparation Example 1. The resultant water-soluble polyester resin(hereinafter referred to as “resin solution B”) has an acid value of 30 mg KOH/g, a weight average molecular weight of 12,000, a softening point of 95° C., and pH of 8.7.

A mixture composed of 3 grams of carbon black(PRINTEX 150T), 0.5 grams of charge control agent(BONTRON S-34), and 30 grams of distilled water is added to 100 grams of the resin solution B and dispersed by a fast distributor to form colored resin dispersions. The colored resin dispersions are mixed with release agents and again dispersed. Another reactor is charged with an aqueous solution which 5 grains of hydrochloric acid is mixed with 100 grams of distilled water. Then, the colored resin dispersions are slowly added to the reactor with fast stirring at 50° C. so that toner particles are formed by a suspension process accompanied with reverse-neutralization. The resultant potato-shaped toner particles have 10 μm of particle diameter and 1.31 GSD of average volume diameter. The obtained toner particles are washed, filtrated, and dried. Subsequently, 100 grams of the died toner particle composition is mixed with 1 gram of hydrophobic silica(Degussa R972) by means of Henschel mixer to produce a toner for electrostatic development. A rebuilt toner cartridge (Laser printer ML6060 made in Samsung Electronics Co., Ltd) filled with said toner provides a very clear and high quality image.

PREPARATION EXAMPLE 3

Crushed waste PET chips (400 g), rosin ester (200 g), monobutyl tartaric acid (0.3 g), fumaric acid (150 g), neopentyl glycol (10 g) and diethylene glycol (100 g) are placed in a reactor which is equipped with an agitator, a reflux condenser, a separator, a thermometer and a nitrogen injection port. The reaction method is the same with Preparation Example 1, except that 55 grams of potassium hydroxide is used as a neutralizer instead of sodium hydroxide. The resultant water-soluble polyester resin (hereinafter referred to as “resin solution C”) has an acid value of 28 mg KOH/g, a weight average molecular weight of 12,000, a softening point of 105° C., and pH of 8.1.

A mixture composed of 3 grams of carbon black(PRINTEX 150T), 0.5 grams of charge control agent(BONTRON S-34), and 30 grams of distilled water is added to 100 grams of the resin solution C and dispersed by a fast distributor to form colored resin dispersions. The colored resin dispersions are mixed with release agents and again dispersed. Another reactor is charged with an aqueous solution which 5 grams of hydrochloric acid is mixed with 100 grams of distilled water. Then, the colored resin dispersions are slowly added to the reactor with fast stirring at 50° C. so that toner particles are formed by a suspension process accompanied with reverse-neutralization. The resultant potato-shaped toner particles have 11 μm of particle diameter and 1.31 GSD of average volume diameter. The obtained toner particles are washed, filtrated, and dried. Subsequently, 100 grams of the dried toner particle composition is mixed with 1 gram of hydrophobic silica(Degussa R972) by means of Henschel mixer to produce a toner for electrostatic development. A rebuilt toner cartridge (Laser printer ML6060 made in Samsung Electronics Co., Ltd) filled with said toner provides a very clear and high quality image.

PREPARATION EXAMPLE 4

Crushed waste PET chips (350 g), maleic gum rosin (250 g), monobutyl tartaric acid (0.3 g), trimellitic anhydride (10 g), neopentyl glycol (50 g) and ethylene oxide adduct of bisphenol A (150 g) are placed in a reactor which is equipped with an agitator, a reflux condenser, a separator, a thermometer and a nitrogen injection port. The reaction method is the same with Preparation Example 1. The resultant water-soluble polyester resin(hereinafter referred to as “resin solution D”) has an acid value of 45 mg KOH/g, a weight average molecular weight of 11,500, a softening point of 81° C., and pH of 8.7.

A mixture composed of 3 grams of carbon black(PRINTEX 150T), 0.5 grams of charge control agent(BONTRON S-34), and 30 grams of distilled water is added to 100 grams of the resin solution D and dispersed by a fast distributor to form colored resin dispersions. The colored resin dispersions are mixed with release agents and again dispersed. Another reactor is charged with an aqueous solution which 5 grams of hydrochloric acid is mixed with 100 grams of distilled water. Then, the colored resin dispersions are slowly added to the reactor with fast stirring at 50° C. so that toner particles are formed by a suspension process accompanied with reverse-neutralization. The resultant potato-shaped toner particles have 8 μm of particle diameter and 1.29 GSD of average volume diameter. The obtained toner particles are washed, filtrated, and dried. Subsequently, 100 grams of the dried toner particle composition is mixed with 1 gram of hydrophobic silica(Degussa R972) by means of Henschel mixer to produce a toner for electrostatic development. A rebuilt toner cartridge (Laser printer ML6060 made in Samsung Electronics Co, Ltd) filled with said toner provides a very clear and high quality image.

PREPARATION EXAMPLE 5

50 grams of the polyester resin aqueous solution from Preparation Example 1 is added to a mixture composed of 3 grams of carbon black(PRINTEX 150T), 0.5 grams of charge control agent (BONTRON S-34), and 30 grams of distilled water, and the mixture is dispersed by a fast distributor to form colored resin dispersions. The colored resin dispersions are mixed with 50 grams of latex from Example 3. The mixture is again dispersed to form colored resin dispersions. Another reactor is charged with a solution which 3.5 grams of hydrochloric acid is mixed with 100 grams of distilled water. Then, the colored resin dispersions are added to the reactor with fast stirring at 50° C. so that toner particles are formed by a suspension process accompanied with reverse-neutralization. The resultant potato-shaped toner particles have 7 μm of particle diameter and 1.29 GSD of average volume diameter The obtained toner particles are washed, filtrated, and dried. Then, 100 grams of the dried toner particle composition is mixed with 1 gram of hydrophobic silica(Degussa R972) by means of Henschel mixer to produce a toner for electrostatic development. A rebuilt toner cartridge (Laser printer ML6060 made in Samsung Electronics Co., Ltd) filled with said toner provides a very clear and high quality image.

PREPARATION EXAMPLE 6

50 grams of the polyester resin aqueous solution from Preparation Example 2 is added to a mixture composed of 3 grams of carbon black(PRINTEX 150T), 0.5 grams of charge control agent (BONTRON S-34), and 30 grams of distilled water, and the mixture is dispersed by a fast distributor to form colored resin dispersions. The colored resin dispersions are mixed with 50 grams of latex from Example 3. The mixture is again dispersed to form colored resin dispersions. Another reactor is charged with a solution which 3.5 grams of hydrochloric acid is mixed with 100 grams of distilled water. Then, the colored resin dispersions are added to the reactor with fast stirring at 50° C. so that toner particles are formed by a suspension process accompanied with reverse-neutralization. The resultant potato-shaped toner particles have 9 μm of particle diameter and 1.33 GSD of average volume diameter. The obtained toner particles are washed, filtrated, and dried. Then, 100 grams of the dried toner particle composition is mixed with 1 gram of hydrophobic silica(Degussa R972) by means of Henschel mixer to produce a toner for electrostatic development. A rebuilt toner cartridge (Laser printer ML6060 made in Samsung Electronics Co., Ltd) filled with said toner provides a very clear and high quality image.

PREPARATION EXAMPLE 7

50 grams of the polyester resin aqueous solution from Preparation Example 3 is added to a mixture composed of 3 grains of carbon black(PRINTEX 150T), 0.5 grams of charge control agent(BONTRON S-34), and 30 grams of distilled water, and the mixture is dispersed by a fast distributor to form colored resin dispersions. The colored resin dispersions are mixed with 50 grams of latex from Example 3. The mixture is again dispersed to form colored resin dispersions. Another reactor is charged with a solution which 3.5 grams of hydrochloric acid is mixed with 100 grams of distilled water. Then, the colored resin dispersions are added to the reactor with fast stirring at 50° C. so that toner particles are formed by a suspension process accompanied with reverse-neutralization. The resultant potato-shaped toner particles have 10 μm of particle diameter and 1.35 GSD of average volume diameter. The obtained toner particles are washed, filtrated, and dried. Then, 100 grams of the dried toner particle composition is mixed with 1 gram of hydrophobic silica(Degussa R972) by means of Henschel mixer to produce a toner for electrostatic development. A rebuilt toner cartridge (Laser printer ML6060 made in Samsung Electronics Co., Ltd) filled with said toner provides a very clear and high quality image.

PREPARATION EXAMPLE 8

50 grams of the polyester resin aqueous solution from Preparation Example 4 is added to a mixture composed of 3 grams of carbon black(PRINTEX 150T), 0.5 grains of charge control agent(BONTRON S-34), and 30 grams of distilled water, and the mixture is dispersed by a fast distributor to form colored resin dispersions. The colored resin dispersions are mixed with 50 grams of latex from Example 3. The mixture is again dispersed to form colored resin dispersions. Another reactor is charged with a solution which 3.5 grams of hydrochloric acid is mixed with 100 grams of distilled water Then, the colored resin dispersions are added to the reactor with fast stirring at 50° C. so that toner particles are formed by a suspension process accompanied with reverse-neutralization. The resultant potato-shaped toner particles have 8 μm of particle diameter and 1.26 GSD of average volume diameter. The obtained toner particles are washed, filtrated, and dried. Then, 100 grams of the dried toner particle composition is mixed with 1 gram of hydrophobic silica(Degussa R972) by means of Henschel mixer to produce a toner for electrostatic development. A rebuilt toner cartridge (Laser printer ML6060 made in Samsung Electronics Co., Ltd) filled with said toner provides a very clear and high quality image.

PREPARATION EXAMPLE 9

50 grams of the polyester resin aqueous solution from Preparation Example 1 is added to a mixture composed of 3 grams of carbon black (PRINTEX 150T), 0.5 grams of charge control agent(BONTRON S-34), and 30 grams of distilled water, and the mixture is dispersed by a fast distributor to form colored resin dispersions. The colored resin dispersions are mixed with 50 grams of latex from Example 4. The mixture is again dispersed to form colored resin dispersions. Another reactor is charged with a solution which 3.5 grams of hydrochloric acid is mixed with 100 grams of distilled water. Then, the colored resin dispersions are added to the reactor with fast stirring at 50° C. so that toner particles are formed by a suspension process accompanied with reverse-neutralization. The resultant potato-shaped toner particles have 9 μm of particle diameter and 1.27 GSD of average volume diameter. The obtained toner particles are washed, filtrated, and dried. Then, 100 grams of the dried toner particle composition is mixed with 1 gram of hydrophobic silica(Degussa R972) by means of Henschel mixer to produce a toner for electrostatic development. A rebuilt toner cartridge (Laser printer ML6060 made in Samsung Electronics Co., Ltd) filled with said toner provides a very clear and high quality image.

Industrial Applicability

Thus, the making method of a toner for electrostatic development according to present invention can easily and rapidly produce a toner composition through a suspension process accompanied with reverse-neutralization. The toner according to the present invention has fine particles with diameter of less than 10 μm and narrow particle distribution of 1.30 GSD. Accordingly, the toner of the present invention has excellent fusing and separation property and desirable offset property, and does not generate fog and deterioration of toner according to wear by use. In addition, because the toner of the present invention can be again dissolved in a basic solution to form toner particles through a suspension process accompanied with reverse-neutralization, it is possible to recycle waste toners. 

1. A method for making a toner for electrostatic development by a suspension process accompanied with reverse-neutralization, the method comprising: phase 1 for producing a linear low molecular weight polymer having carboxyl groups (—COOH) at the end of a polymer chain; phase 2 for producing a water-dispersible resin composition to function as a dispersant by adding basic compounds to the linear low molecular weight polymer to neutralize and adding distilled water; phase 3 for producing a cross-linked high molecular weight water-dispersible latex, separately; phase 4 for producing colored resin dispersions by adding additives such as a colorant, charge control agents, and release agents to the water-dispersible resin composition from the phase 2, dispersing the additives using high shear force, adding the cross-linked high molecular weight water-dispersible latex from the phase 3, and mixing and dispersing the cross-linked latex; phase 5 for producing toner particles by putting the colored resin dispersions from the phase 4 into an aqueous solution containing acid compounds to carry out a suspension process accompanied with reverse-neutralization using high shear force, and heating and stabilizing the solution; phase 6 for producing a colored toner particle composition by filtrating and washing the toner particles from the phase 5 two or three times, repeatedly, and carrying out vacuum drying; and phase 7 for adding hydrophobic silica to the colored toner particle composition from the phase 6 and blending the hydrophobic silica with the colored toner particle composition using a powder mixer.
 2. The method of claim 1, wherein the linear low molecular weight polymer in the phase 1 is made of monomers such as aromatic vinyl-based monomers including styrene, acrylate-based monomers, and monomers possible to copolymerize with the aromatic vinyl-based monomers or acrylate-based monomers.
 3. The method of claim 1 or claim 2, wherein the linear low molecular weight polymer has a number-average molecular weight of 5,000˜50,000.
 4. The method of claim 1 or claim 2, wherein the linear low molecular weight polymer has 10˜110 mg KOH/g of acid value.
 5. The method of claim 2, wherein the linear low molecular weight polymer comprises 30˜90 w % of styrene or 5˜90 w % of acrylate.
 6. The method of claim 1, wherein the material to be added in order to combine carboxyl groups to the end of a polymer chain is selected from the group of (meta) acrylic acid, maleic anhydride, maleic rosin, fumaric acid, and itaconic acid.
 7. The method of claim 1 or claim 6, wherein the amount of the material used to combine carboxyl groups to the end of a polymer chain is 5˜50 w %, based on the total amount of monomer mixture.
 8. The method of claim 1, wherein the linear low molecular weight polymer having carboxyl groups (—COOH) at the end of a polymer chain includes a polyester resin composition.
 9. The method of claim 8, wherein the polyester resin composition is produced through the phases comprising: a phase for producing a linear low molecular weight polyester resin composition through a first reaction, which produce a low molecular weight polymer using linear structure forming accelerant; and a phase for carrying out a second reaction by adding polybasic acids to the linear low molecular weight polyester resin composition so that the polyester resin has two or three carboxyl groups at the end of the polymer chain.
 10. The method of claim 8, wherein the polyester resin composition can be produced from depolymerization of a waste polyester.
 11. The method of claim 10, wherein the linear low molecular weight polyester resin composition is produced according to the phases comprising: a phase for depolymerizing a waste polyester resin using a solid resin dissolvent; a phase for carrying out a second depolymerization adding polybasic acids; and a phase for carrying out a polycondensation reaction using polyhydric alcohols and a tin-based catalyst.
 12. The method of claim 11, wherein the solid resin dissolvent is selected from the group of gum rosin, wood rosin, dehydrogenated rosin, hydrogenated rosin, maleic rosin, rosin ester, pinene resin, dipentene resin, C5 petroleum resins, C9 petroleum resins, dammar resin, copal resin, dicyclopentadien (hereinafter referred to as “DCPD”) resin, hydrogenated DCPD resin, styrene maleic resin, and a mixture thereof.
 13. The method of claim 11, wherein the weight ratio of the waste polyester resin to the solid resin dissolvent is 1:9˜9:1.
 14. The method of claim 1, wherein the basic compound to be used in the phase 2 is selected from the group of sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonium hydroxide, and amines.
 15. The method of claim 1 or claim 14, wherein the amount of the basic compound to be used in the phase 2 is 5˜50 w %, based on the amount of the linear low molecular weight polymer from the phase
 1. 16. The method of claim 1, wherein the high molecular weight water-dispersible latex from the phase 3 has 100,000˜1,000,000 weight average molecular weight.
 17. The method of claim 1, wherein the high molecular weight water-dispersible latex from the phase 3 has 5˜50 w % of gel content.
 18. The method of claim 1, wherein the acid compound to be used in the phase 5 is selected from the group of hydrochloric acid, sulfuric acid, nitric acid, acetic acid, formic acid, oxalic acid, fluoric acid, phosphoric acid, bromic acid, and p-toluene sulfonic acid.
 19. The method of claim 1 or claim 18, wherein the amount of the acid compound to be used in the phase 5 is 5˜50 w %, based on the amount of the colored resin dispersions.
 20. The method of claim 1, wherein, if the particles of the colored toner particle composition from the phase 6 are bad, the particles are filtrated and again inputted to the phase 2, and are retreated according to the same phases with claim
 1. 21. The method of claim 1, wherein the amount of the hydrophobic silica to be used in the phase 7 is 15 w %, based on 100 grams of the colored toner particle composition from the phase
 6. 22. A method for making a toner for electrostatic development by a suspension process accompanied with reverse-neutralization, the method comprising: phase 1 for producing linear low molecular weight polyester resin composition having carboxyl groups (—COOH) at the end of a polymer chain; phase 2 for producing polyester resin aqueous solution to function as a dispersant by adding basic compound and distilled water to the low molecular weight polyester resin composition; phase 3 for producing cross-linked ethylene-based copolymerization latex; phase 4 for producing colored resin dispersions by mixing the polyester resin aqueous solution from the phase 2 with a colorant, charge control agents, and release agents, adding the cross-linked ethylene-based copolymerization latex from the phase 3, and mixing and dispersing the cross-linked latex; phase 5 for producing toner particles, by putting the colored resin dispersions from the phase 4 into an aqueous solution containing acid compounds to carry out a suspension process accompanied with demineralization reaction using high shear force, and heating the solution; phase 6 for producing a colored toner particle composition, by filtrating and washing the toner particles from the phase 5 and carrying out vacuum drying; and phase 7 for adding hydrophobic silica or titanium oxide to the colored toner particle composition from the phase 6 at the amount of 1˜5 w %, based on 100 grams of the colored toner particle composition, and blending the silica with the colored toner particle composition using a powder mixer.
 23. The method of claim 22, wherein the linear low molecular weight polyester resin composition having carboxyl groups at the end of a polymer chain is produced through the phases comprising: a phase for producing a linear low molecular weight polyester resin composition through a first reaction, which produce a low molecular weight polymer using linear structure forming accelerant; and a phase for carrying out a second reaction by adding polybasic acid to the linear low molecular weight polyester resin composition so that the polyester resin has two or three carboxyl groups at the end of a polymer chain.
 24. The method of claim 22, the linear low molecular weight polyester resin composition having carboxyl groups at the end of a polymer chain can be produced from depolymerization of a waste polyester resin.
 25. A method for making a toner for electrostatic development by a suspension process accompanied with reverse-neutralization, the method comprising: phase 1 for comprising a sub-phase 1(a) for depolymerizing a waste polyester resin by using a solid resin dissolvent, a sub-phase 1(b) for carrying out second depolymerization by adding polybasic acids, and a sub-phase 1(c) for carrying out polycondensation reaction by using polyhydric alcohols and a tin-based catalyst; phase 2 for producing polyester resin aqueous solution to function as a dispersant by adding basic compound and distilled water to the low molecular weight polyester resin composition; phase 3 for producing cross-linked ethylene-based copolymerization latex; phase 4 for producing colored resin dispersions, by mixing the polyester resin aqueous solution from the phase 2 with a colorant, charge control agents, and release agents, adding the cross-linked ethylene-based copolymerization latex from the phase 3, and mixing and dispersing the cross-linked latex; phase 5 for producing toner particles, by putting the colored resin dispersions from the phase 4 into an aqueous solution containing acid compounds to carry out a suspension process accompanied with demineralization reaction using high shear force, and heating the solution; I phase 6 for producing a colored toner particle composition, by filtrating and washing the toner particles from the phase 5 and carrying out vacuum drying; and phase 7 for adding hydrophobic silica or titanium oxide to the colored toner particle composition from the phase 6 at the amount of 1˜5 w %, based on 100 grams of the colored toner particle composition, and blending the silica with the colored toner particle composition using a powder mixer.
 26. The method of claim 25, wherein the solid resin dissolvent to depolymerize a waste polyester is selected from the group of gum rosin, wood rosin, dehydrogenated rosin, hydrogenated rosin, maleic rosin, rosin ester, pinene resin, dipentene resin, C5 petroleum resins, C9 petroleum resins, dammar resin, copal resin, DCPD resin, hydrogenated DCPD resin, styrene maleic resin, and a mixture thereof.
 27. The method of claim 25, wherein the weight ratio of the waste polyester to the solid resin dissolvent is 1:9˜9:1.
 28. A toner for electrostatic development being produced according to the claim 1, claim 23 or claim 26, the toner for electrostatic development being produced by a suspension process accompanied with reverse-neutralization. 